The offspring of female rats injected during pregnancy with Methylazoxymethanol acetate (MAM) develop a markedly reduced cerebral neocortex. This chemically induced micrencephaly does not appear to severely alter normal rat behavior patterns since similarly treated animals are capable of learning, reproduce successfully, and may exhibit many other species typical behaviors. However, these behaviors have been observed only in relatively restricted laboratory cage environments which may present no real challenge to the survival of a micrencephalic individual. It is the purpose of this study to examine the behavior of micrencephalic rats living as free ranging groups in large, complexly structured environments. It is anticipated that, initially MAM-treated animals will exhibit behavioral deficits and may not be capable of fully utilizing the complex environments until long after normal animals, thereby indicating that one of the roles of the neocortex is to facilitate the rapid, full utilization of new and complex environments.